Problem: Simplify the following expression: $k = \dfrac{5a}{2} - \dfrac{a}{4}$
Explanation: In order to subtract expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $2$ and $4$ $\lcm(2, 4) = 4$ $ k = \dfrac{2}{2} \cdot \dfrac{5a}{2} - \dfrac{1}{1} \cdot \dfrac{a}{4} $ $k = \dfrac{10a}{4} - \dfrac{a}{4}$ $k = \dfrac{10a -a}{4}$ $k = \dfrac{9a}{4}$